This application is based on and claims the priority under 35 U.S.C. xc2xa7119 of German Patent.Applications 199 40 200.0 and 199 40 201.9, both filed on Aug. 25, 1999, the entire disclosure of which is incorporated herein by reference.
The invention relates to a pyrotechnic ignition system with an integrated ignition circuit, especially for triggering or activating an occupant restraint system in a vehicle.
Pyrotechnical ignition systems are used in particular for triggering occupant restraint systems, but in principle they can also be used for military applications or in mining. A pyrotechnical fuel or explosive charge is ignited by releasing energy from an igniter. This energy is supplied electrically in the form of an ignition voltage which is generated and/or stored in an integrated ignition circuit by means of electrical components.
An ignition system of this kind, for example, is described in German Patent Document DE 37 17 149 C3 where it is described under the term detonator ignition element. Here too, electrical components are used, in particular an electronic circuit which includes an overvoltage protector, a communications unit, a timer and interlock circuit, as well as a self-test module. For storing energy, an ignition capacitor is used which, because of its size, is not integrated in the circuit but provided as a separate component.
In ignition systems with integrated ignition circuits without an ignition capacitor, as for example presented in the article by Willis, K.: An Introduction to Semiconductor Initiation of Electroexplosive Devices, in; 2nd International Symposium on Sophisticated Car Occupant Safety Systems, Airbag 2000, Karlsruhe, Germany, 1994, pp. 42-1 to 42-9, the ignition energy must be supplied to the integrated circuit in the ignition system at the time of triggering. Consequently the available ignition energy, the triggering velocity and the triggering safety are diminished.
The published German Patent Applications DE 35 37 820 A1 and DE 196 53 115 A1 each present an ignition unit for igniting a pyrotechnical fuel pellet where not only an electrically ignitable igniter but also an ignition energy storage unit and an interlock unit are together integrated on a semiconductor chip, the interlock unit causing discharging of the energy storage unit via the electrical igniter by means of an unlocking signal. It is, however, not sufficient to use semiconductor capacitors for storing energy, at least for many igniters.
The integration of electrical components in a pyrotechnical ignition element is also described in German Patent Document DE 196 10 799 C1, wherein a printed-conductor structure is punched from a metal strip and bent three dimensionally. These printed conductors are fully enclosed by injection molding with a cuboidal carrier body, and subsequently, components can be inserted in recesses and connected to the printed conductors. The voluminous ignition energy capacitor is stowed in a space-saving manner in a cavity inside the carrier body. Also, an integrated circuit is provided for triggering. The module is then encased in a housing. The cost of manufacturing such an ignition element and the susceptibility to fault is very high on account of the filigreed construction.
Published German Patent Application DE 198 46 110 A1 shows the use of separate substrates (7, 8) as carrier elements for an ignition system with electrical components (9) that are arranged on both sides on the two substrates (7 and 8) arranged parallel to and at a distance from each other (compare, for instance, FIG. 1 and col. 2, line 45 ff.). In the interest of a space-saving construction, the components (9) situated on the two sides facing each other of the substrates (7 and 8) are placed extremely close together. A direct connection of these components (9) facing each other on the substrates (7, 8) is not disclosed, however, and would normally lead to an electrical defect or a short circuit.
The basic concept and object of the invention is to use an existing electrical component, having at least one flat external surface that at least in zones is itself non-conductive, as a carrier element for the other components of the integrated ignition circuit of a pyrotechnic ignition system and to locate the other components on this flat external surface. In view of the inventive solution, an otherwise usual additional carrier element in the form of a printed-circuit board or a cuboidal carrier element according to German Patent Document 196 10 799 C1, is not required. Thus, not only material but also space is saved, the manufacturing is simplified and hence reliability is enhanced.
According to the invention, a capacitor arrangement, such as the plate capacitor arrangement of an ignition capacitor, is particularly suitable as a carrier element for directly carrying other components in a most advantageous way because of the considerable size and the flat external surface thereof. Based on this, numerous further inventive developments result with respect to the arrangement and modification to the design of the printed-conductor structure and the ignition layer. Throughout this description, the term xe2x80x9cprinted-conductor structurexe2x80x9d is used generally to refer to any conductor structure whether or not the conductor paths or traces are printed i.e. deposited conductors, or alternatively insertable metal strip conductors. Thus, with respect to the arrangement and embodiment of the design of the printed-conductor structure, a simple design is proposed wherein the conductors are actually formed by insertable metal parts in the housing, or for the printed-conductor structure to be vapor-deposited, precipitated or bonded on the housing or on external surfaces of the capacitor arrangement that are themselves non-conducting.
In conjunction with the housing, the insertable metal parts in turn permit an extremely compact and simple construction and can be used both for the connection between capacitor arrangement and circuit and even to the external terminals. In a particularly preferred further development, the external terminals can even be formed out of these insertable parts directly or integrally.
An arrangement of the printed-conductor structure on the carrier element permits the creation of contact zones that are linked to corresponding contact zones of the circuit. It is particularly advantageous to assemble circuits as components in the form of unpackaged semiconductor chips, so-called naked chips without a housing, or in flip-chip technology with their structured side that has contact zones facing downward on the printed-conductor structure. The printed-conductor structure can also be used on the lateral surfaces of the capacitor arrangement for linking up the individual capacitor electrodes or to establish a connection to other contact zones, with which the ignition system is connected via assigned or allocated contact elements, in the inside of the housing with an electronic triggering unit, for example a central unit of an occupant restraint system.
As regards the arrangement and embodiment of the design of the ignition layer, provision is made for it to be arranged on the carrier element, that is in particular on the capacitor arrange-ment in electrical connection with the printed conductors situated there, or alternatively an arrangement on the circuit or a modification to the design directly on this circuit, for instance as a silicon bridge igniter.
These variants relating to the arrangement and modifications to the design of the printed-conductor structure and the ignition layer are independent of each other and can therefore be combined at will.
Furthermore, extremely advantageous further developments are possible with respect to the design of the housing and the external terminals.